Abstract
BackgroundHigh dietary protein can reduce fat deposition in animal subcutaneous adipose tissue, but little is known about the mechanism.MethodsSixty 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.ResultsHP 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 γ (PPARγ) 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 PPARγ 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.ConclusionFat 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.
Highlights
High dietary protein can reduce fat deposition in animal subcutaneous adipose tissue, but little is known about the mechanism
The present study showed that high dietary protein reduced the mRNA abundance or protein expression level of lipogenic genes such as acetyl CoA carboxylase (ACC), malic enzyme (ME), glucose-6-phosphate dehydrogenase (G-6-PDH) and SREBP-1 during the whole growth period
Our results show that high dietary protein increased Lipoprotein lipase (LPL) mRNA expression and enzyme activity at 60 kg, which suggests that more free fatty acids (FFA) was released from VLDL at this weight
Summary
High dietary protein can reduce fat deposition in animal subcutaneous adipose tissue, but little is known about the mechanism. The synthesis of subcutaneous adipose tissue triglycerides the major constituents of depot fat - either proceeds from fatty acids synthesized de novo in that tissue [2,3]. Processes that determine fat deposition in adipose tissue include the rates of fat uptake, de novo fatty acid synthesis, triacylglycerol synthesis, lipid degradation and transport processes of fatty acids [5]. Sterol regulatory element binding protein 1(SREBP-1), peroxisome proliferator-activated receptor g (PPARg) and adipose fatty acids-binding protein (A-FABP, known as FABP4), have recently been identified as being implicated in lipid metabolism in adipose tissue by regulating gene expression of enzymes or proteins involved in lipid metabolism, or by transporting fatty acids [14,15,16,17,18]
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