Role of Bone Morphogenetic Protein 4 in the Differentiation of Brown Fat-

25 There are 2 different types of fat present in mammals: white adipose tissue, the primary site of 26 energy storage, and brown adipose tissue, which is specialized in energy expenditure. Factors 27 that specify the developmental fate and function of brown fat are poorly understood. Bone 28 morphogenic proteins (BMPs) play an important role in adipogenesis. While BMP4 is capable of 29 triggering commitment of stem cells to the white adipocyte lineage, BMP7 triggers commitment 30 of progenitor cells to a brown adipocyte lineage and activates brown adipogenesis. To investigate 31 the differential effects of BMPs on the development of adipocytes, C3H10T1/2 pluripotent cells 32 were pretreated with BMP4 and BMP7, followed by different adipogenic induction cocktails. 33 Both BMP4 and BMP7 unexpectedly activated a full program of brown adipogenesis, including 34 induction of the brown-fat-defining marker uncoupling protein 1 (UCP1), increasing the 35 expression of early regulators of brown fat fate PRDM16 (PR-domain-containing 16), and 36 induction of mitochondrial biogenesis and function. Implantation of BMP4-pretreated 37 C3H10T1/2 cells into nude mice resulted in the development of adipose tissue depots containing 38 UCP1-positive brown adipocytes. Interestingly, BMP4 could also induce brown fat-like 39 adipocytes in both white and brown preadipocytes, thereby decreasing the classical brown 40 adipocyte marker, Zic1, and increasing the recently identified beige adipocyte marker, TMEM26. 41 The data indicate an important role of BMP4 in promoting brown adipocyte differentiation and 42 thermogenesis in vivo and in vitro, and offers a potentially new therapeutic approach for the 43 treatment of obesity. 44