UCP1 and hypothyroidism: In BAT, we found reduced Klf9 (−34.82%) expression and 2.51-fold increased mRNA levels of Ucp1, the master regulator of brown adipocyte thermogenesis, although Prdm16, the transcriptional coregulator of brown adipocyte differentiation, and Ppargc1a were not regulated by hypothyroidism (Figure 4H).