Expression of uncoupling protein 1 in bovine muscle cells1

Abstract

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 ( < 0.05), while those in cells cultured in adipogenic medium were decreased ( < 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 ( < 0.05) and were decreased when cells were cultured in adipogenic medium ( < 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.

Regulatory expression of uncoupling protein 1 and its related genes by endogenous activity of the transforming growth factor‐β family in bovine myogenic cells

“…Immunohistochemical studies showed positive staining for UCP1 at the peripheral region of muscle fibres but not in adipocytes resident in the skeletal muscle. Expression levels of Ucp1 were higher in myosatellite cells cultured under the myogenic condition than in those under the adipogenic condition 3 . These results suggest that bovine myogenic cells express Ucp1 .…”

“…We previously demonstrated that bovine Ucp1 expression is increased with progression of myogenesis, with levels significantly higher on day 12 than on day 6, after induction of myogenesis in myosatellite cells 3 . Endogenous TGF‐β/activin pathway negatively regulates murine myogenesis 19,29 .…”

“…The expression of muscular Ucp1 was markedly lower than the expression in the brown fat of calves 3 . However, considering the large mass of skeletal muscles, UCP1‐mediated muscular thermogenesis may have a significant impact on energy metabolism.…”

“…All animal experiments were conducted in accordance with the approved guidelines. Bovine myosatellite cells were isolated from the musculus longissimus cervicis of Japanese Black steers aged 30 months ( n = 3) as described previously 3 . Primary myosatellite cells were passaged once and frozen (passage 2) in cell freezing medium (Bambanker, Nippon Genetics, Tokyo, Japan), and stored in liquid nitrogen.…”

“…The uncoupling occurs through mitochondrial expression of uncoupling protein 1 (UCP1), predominantly expressed in brown/beige adipocytes 1,2 . Recently, we demonstrated significant expression of Ucp1 in bovine skeletal muscles through reverse transcription (RT)‐polymerase chain reaction (PCR) analyses 3 . Immunohistochemical studies showed positive staining for UCP1 at the peripheral region of muscle fibres but not in adipocytes resident in the skeletal muscle.…”