Ambient temperature regulates uncoupling protein 1 expression but fails to induce adipocyte browning in zebrafish

Adipocyte browning is a potential strategy to treat obesity. Although uncoupling protein 1 (UCP1) plays an important role in browning and thermogenesis in mammals, it is not known for zebrafish. We found that cold stress, as an efficient way of inducing browning in mammals, failed to induce adipocyte browning in zebrafish, evidenced by the cell morphology and expression of browning genes. Other potential approaches including heat stress and treatment with a chemical known to induce adipocyte browning in mammals also failed to induce browning, suggesting that zebrafish may not be a suitable model to study the browning process. Interestingly however, we found that the liver expresses ucp1 much higher than the adipose tissue in zebrafish. Moreover, the expression of ucp1 in the zebrafish liver is positively regulated by the ambient temperature. These findings suggest that the role of ucp1 in zebrafish may be different from its established role in adipocyte browning in mammals but instead be evolved to adapt to environmental temperature.