Certain white adipose tissue (WAT) depots are readily able to convert to a ''brown-like'' state with prolonged cold exposure or exposure to b-adrenergic compounds. This process is characterized by the appearance of pockets of uncoupling protein 1 (UCP1)-positive, multilocular adipocytes and serves to increase the thermogenic capacity of the organism. We show here that fibroblast growth factor 21 (FGF21) plays a physiologic role in this thermogenic recruitment of WATs. In fact, mice deficient in FGF21 display an impaired ability to adapt to chronic cold exposure, with diminished browning of WAT. Adipose-derived FGF21 acts in an autocrine/paracrine manner to increase expression of UCP1 and other thermogenic genes in fat tissues. FGF21 regulates this process, at least in part, by enhancing adipose tissue PGC-1a protein levels independently of mRNA expression. We conclude that FGF21 acts to activate and expand the thermogenic machinery in vivo to provide a robust defense against hypothermia.

The worldwide epidemic of obesity has increased the urgency of developing a deeper understanding of physiological systems related to energy balance and energy storage, including the mechanisms controlling the development of fat cells (adipocytes). The differentiation of committed preadipocytes to adipocytes is controlled by PPARγ and several other transcription factors 1, but the molecular basis for preadipocyte determination is not understood. Using a novel method for the quantitative analysis of transcriptional components, we identified the zinc-finger protein Zfp423 as a factor enriched in preadipose versus non-preadipose fibroblasts. Ectopic expression of Zfp423 in non-adipogenic NIH 3T3 fibroblasts robustly activates expression of PPARγ in undifferentiated cells and permits cells to undergo adipocyte differentiation under permissive conditions. ShRNA-mediated reduction of Zfp423 expression in 3T3-L1 cells blunts preadipocyte PPARγ expression and diminishes the ability of these cells to differentiate. Furthermore, both brown and white adipocyte differentiation is strikingly impaired in Zfp423-deficient mouse embryos. Zfp423 regulates PPARγ expression, in part, through amplification of the BMP signaling pathway, an effect dependent on the SMAD binding capacity of Zfp423. This study identifies Zfp423 as a transcriptional regulator of preadipocyte determination.

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Summary PGC1α is a key transcriptional coregulator of oxidative metabolism and thermogenesis. Through a high throughput chemical screen, we found that molecules antagonizing the TRPVs (Transient Receptor Potential Vanilloid), a family of ion channels, induced PGC1α expression in adipocytes. In particular, TRPV4 negatively regulated the expression of PGC1α, UCP1 and cellular respiration. Additionally, it potently controlled the expression of multiple proinflammatory genes involved in the development of insulin resistance. Mice with a null mutation for TRPV4 or wild-type mice treated with a TRPV4 antagonist showed elevated thermogenesis in adipose tissues and were protected from diet-induced obesity, adipose inflammation and insulin resistance. This role of TRPV4 as a cell-autonomous mediator for both the thermogenic and proinflammatory programs in adipocytes could offer a new target for treating obesity and related metabolic diseases.