Uncoupling protein1 mRNA, mitochondrial GTP-binding, and T4 5′-deiodinase of brown adipose tissue in euthermic Daurian ground squirrel during cold exposure

Regulation of thermogenic activity and uncoupling protein1 (UCP1) expression in brown adipose tissue (BAT) were studied in euthermic Daurian ground squirrel after acute and chronic cold exposure at 4°C. The UCP1 concentration was indirectly determined by titration with its specific ligand [³H]-labeled GTP, and Ucp1 mRNA was detected by using a [³²P]-labeled antisense oligonucleotide probe. Both acute and chronic cold exposure stimulated up-regulation of Ucp1 mRNA. Although UCP1 concentration is not significantly increased after 24 h of cold exposure, it is markedly elevated by 75% in squirrels after 4-week cold adaptation compared with controls raised at 22°C. Changes in T₄ 5′-deiodinase activity were closely associated with variations of Ucp1 mRNA level. Ucp1 gene expression is significantly affected by cold exposure in BAT from euthermic Daurian ground squirrels. In addition, the activation of T₄ 5′-deiodinase may be an important regulatory factor in cold-induced Ucp1 expression.