Possibility of uncoupling protein 1 expression in bovine fast-twitch muscle fibers.

Uncoupling protein 1 (UCP1) is responsible for non-shivering thermogenesis in brown/beige adipocytes in humans and rodents. Previously, we showed unexpected expression of UCP1 in bovine skeletal muscles. Here we evaluated Ucp1 mRNA levels in the muscle tissue of Japanese Black steers. Expression of Ucp1 was higher in 30-month-old cattle than in 26-month-old cattle. Levels of myosin heavy chain (Myh)1, an MYH predominantly expressed in fast-twitch muscles, were also significantly higher in cattle aged 30 months. A similar tendency was observed in the expression of other Myhs that are highly expressed in fast-twitch muscles, Myh2 and Myh4. Ucp1 expression was positively correlated with expression of Myh1, Myh2, and Myh4. Our results indicate the possibility of Ucp1 expression in fast-twitch muscle fibers.