Changes in UCP family expressions in rat tissues due to diet and aging

Regulation of the gene expressions of uncoupling proteins (UCP)-1, 2 and 3 was investigated in the white and brown adipose tissues and skeletal muscle of young and old rats (8-wk- and 8-mo-old, respectively) fed diets containing various fats (hydrogenated fat, corn oil or fish oil) and proteins (casein or soybean) for 1 wk. The mRNA expressions of UCP-1, 2 and 3 were elevated in the white adipose tissues of the young rats fed soybean protein as compared to those fed casein, and that of UCP-2 was also elevated in the brown adipose tissue. The effects of dietary fat type on the expressions were not clear. The UCP-1, 2 and 3 mRNA expressions were markedly reduced in the tissues of the old rats. The UCP-2 expressions were more markedly elevated by dietary soybean protein and reduced by aging than the others, particularly in the white adipose tissue. The expressions of leptin involved in thermogenesis were also reduced by aging. Moreover, in a fasted-refed experiment conducted for the young rats, UCP-2 mRNA induction in the white adipose tissues reached maximal levels at 1 or 2 h and was stimulated by dietary fat or soybean protein. Thus, UCP-2 mRNA expression was markedly affected by diet and aging, particularly in white adipose tissue.