Long-term dietary high protein intake up-regulates tissue specific gene expression of uncoupling proteins 1 and 2 in rats.
BACKGROUND
The consequences of chronic high protein (HP) diets are discussed controversially and are not well understood. Rats adapted to HP exposure show an increased amino acid and fat oxidation and lower feed energy efficiency. We hypothesized that the dietary protein level can affect gene expression of uncoupling protein (UCP) homologues which is suggested to be involved in thermogenesis, substrate oxidation, and energy expenditure.


OBJECTIVE
To assess the mRNA expression of UCP homologues in various tissues of rats fed HP diets and to relate UCP gene expression to various parameters of substrate and energy metabolism. To obtain further indications for the possible involvement of UCP in reducing feed energy efficiency under conditions of HP exposure.


METHODS
Adult rats were adapted to casein based diets containing either 13.8% (adequate, AP), 25.7% (medium, MP), or 51.3 % (high, HP) crude protein. Rats were fed for 8 wk and killed in the postabsorptive state. Energy expenditure and mRNA expression were measured using indirect calorimetry and Northern blot analysis, respectively. Pearson correlation coefficients were calculated to determine relationships between UCP mRNA expression and metabolic parameters.


RESULTS
Hepatic UCP2 mRNA expression was increased by MP and HP diets compared to AP diet. In skeletal muscle UCP2 mRNA expression was lowest under MP conditions. UCP1 mRNA expression in brown adipose tissue (BAT) was significantly increased by HP exposure. The values were inversely associated with feed energy efficiency and positively with energy expenditure and oxygen consumption in the dark period. Skeletal muscle UCP2 and -3 mRNA expression strongly correlated with the plasma free fatty acid concentration, whereas BAT UCP1 and hepatic UCP2 gene expression did not.


CONCLUSIONS
Our results indicate that hepatic UCP2 and BAT UCP1 mRNA expression is related to the level of dietary protein intake. This suggests a role of UCPs in substrate oxidation and in thermogenesis under conditions of HP exposure.
Petzke
Klaus J
KJ
German Institute of Human Nutrition, Potsdam-Rehbrücke (DIfE), 14558 Nuthetal, Germany. petzke@mail.dife.de
Friedrich
Maika
M
Metges
Cornelia C
CC
Klaus
Susanne
S
D000818:Animals; D015152:Blotting, Northern; D001833:Body Temperature Regulation; D002153:Calorimetry, Indirect; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004734:Energy Metabolism / Q000187:drug effects*; D007473:Ion Channels; D008099:Liver / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D010101:Oxygen Consumption; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D000071256:Uncoupling Protein 1; D000071246:Uncoupling Protein 2; D015854:Up-Regulation
D002352:Carrier Proteins; D004044:Dietary Proteins; D007473:Ion Channels; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D012333:RNA, Messenger; C000604371:UCP1 protein, human; C000604389:UCP2 protein, human; C000604373:Ucp1 protein, rat; C000604391:Ucp2 protein, rat; D000071256:Uncoupling Protein 1; D000071246:Uncoupling Protein 2