Expression of uncoupling protein 1 in bovine muscle cells

Uncoupling protein 1 (Ucp1) is predominantly expressed in brown/beige adipocytes in mammals. Although myogenic cells have been suggested to commit to a brown adipocyte lineage through the induction of Prdm16 expression, Prdm16 is also expressed in skeletal muscle. Thus, we examined expression of Ucp1 in bovine myogenic cells. Considering that Ucp1 is a principle molecule that induces energy expenditure in brown/beige adipocytes, expression of Ucp1 is not preferable in beef cattle because of potential decrease in energy (fattening) efficiency. The RT-PCR analyses revealed the expression of Ucp1 in the skeletal muscle of cattle; expression levels were markedly lower than those in the brown fat of calves. Immunohistochemical analyses showed that Ucp1 surrounded muscle fibers, but not adipocytes residing in skeletal muscle. Myosatellite cells cultured in myogenic medium showed an increase in the expression levels of myogenic regulatory factors (P < 0.05), while those in cells cultured in adipogenic medium were decreased (P < 0.05). The Ucp1 expression was also detected in myosatellite cells; expression levels were greater in cells after myogenic culture for 12 d than in those after myogenic culture for 6 d (P < 0.05) and were decreased when cells were cultured in adipogenic medium (P < 0.05). The Prdm16 expression was not affected by culture conditions, suggesting that the expression of Ucp1 is not regulated by that of Prdm16. The results of the present study provide an insight into the unexpected expression of Ucp1 in bovine skeletal muscle, which suggests the necessity for further studies on Ucp1-mediated energy expenditure in bovine skeletal muscle.