Impact of dietary protein content on uncoupling protein mRNA abundance in swine

The present study was designed to determine if dietary protein can alter uncoupling protein (UCP) expression in swine, as has been shown in rats, and attempt to identify the mechanism. Eight pigs (approximately 50 kg body mass) were fed an 18% crude protein (CP) diet while another eight pigs were switched to a diet containing 12% crude protein (CP) and fed these diets until 110 kg body mass. The outer (OSQ) and middle (MSQ) subcutaneous adipose tissues, liver, leaf fat, longissimus (LM), red portion of the semitendinosus (STR) and the white portion of the ST (STW) were analyzed for gene expression by real-time PCR. Feeding of 12% CP did not alter growth or carcass composition, relative to 18% CP (P>0.05). Serum growth hormone, non-esterified fatty acids, triglycerides and urea nitrogen were reduced with the feeding of 12% CP (P<0.05). The UCP2 mRNA abundance was reduced in LM, STR, MSQ and OSQ with feeding of 12% CP (P<0.05), as was UCP3 mRNA abundance in MSQ and STW (P<0.01). Peroxisome proliferation activated receptor alpha (PPARalpha) and PPARgamma were reduced in MSQ and STR (P<0.05) with feeding 12% CP as was the PPARalpha regulated protein, acyl CoA oxidase (ACOX, P<0.05). These data suggest that feeding 12% CP relative to 18% CP reduces serum NEFA, which reduces PPARalpha and PPARgamma expression and consequently reduces UCP2 lipoperoxidation in OSQ and STR and also reduced UCP3 associated fatty acid transport in MSQ and STW.