UCP1 and obesity due to melanocortin 4 receptor deficiency: We next examined BAT activity and the browning capacity of WAT, which are crucial for regulating energy expenditure and obesity.[6b] We found that brown adipocytes in hRSPO1Tg mice exhibited a remarkably enlarged cell size, expanded lipid droplets, as well as decreased levels of UCP1 protein, a marker of brown/beige adipocytes, when compared with wild‐type mice (Figure 2F).