TRANSCRIPTIONAL REGULATION OF BEIGE ADIPOCYTE CELLULAR PLASTICITY

Obesity is a widespread and growing health problem the United States, associated with metabolic disorders, including diabetes. Major efforts have been made to mitigate obesity through diet control, exercise or appetite suppression. These methods have been met with limited success and high rates of rebound, urging the development of new strategies. Thermogenic beige adipocytes have attracted considerable attention as a new therapeutic target due to their potent anti-obesity activity in adult humans. Unlike classical brown adipocytes that retain a stable cellular identity, beige adipocytes have a unique cellular plasticity, capable of completely interconverting between brown and white adipocyte states via significant epigenomic reprogramming. The extraordinary plastic nature of beige adipocyte cellular identity and its underlying molecular mechanisms have yet to be well understood. Our recent studies led to a striking finding defining the ‘dedifferentiation’ potential of beige adipocytes. We found that upon cold exposure, a subpopulation of whitened beige adipocytes (beige adipocytes turned to white adipocytes), dedifferentiated into progenitor-like cells, proliferated, and possibly redifferentiated into thermogenic adipocytes. This reprogramming process serves as a potential novel mechanism of beige adipocyte recruitment. Our epigenomic analysis identified NFIL3 (Nuclear Factor, Interleukin 3 Regulated) as a key transcription factor, potentially mediating cold-induced beige adipocyte reprogramming. NFIL3 expression was induced by cold exposure, specifically in beige but not in brown adipocytes, and located in dedifferentiating beige adipocytes. Furthermore, both in vitro cell culture and in vivo mouse models deficient with NFIL3 in adipocytes demonstrated that NFIL3 is necessary for adipose tissue browning during cold exposure. In addition, NFIL3 loss in adipocytes resulted in increased susceptibility to diet- induced obesity after high fat diet feeding. Based on these data, we hypothesize that NFIL3 is a key transcription factor that controls beige adipocyte plasticity by mediating the transition from white to brown adipocytes, thereby regulating energy balance and glucose homeostasis. In aim 1, we will elucidate whitened beige adipocyte reprogramming during browning and a role for NFIL3. We will perform beige adipocyte pulse- chase experiments in NFIL3 knockout (KO) mice using microscopy, single nuclei RNA-seq and cell culture. In aim 2, we will determine the role of NFIL3 in cold tolerance and glucose homeostasis by conducting comprehensive physiology studies with adipocyte-specific NFIL3 KO mice. In aim 3, we will identify molecular mechanisms by which NFIL3 regulates adipocyte identity by using ChIP-seq to define the NFIL3 cistrome in beige adipocytes. These studies will uncover novel aspects of beige adipocyte cellular plasticity. We will establish the role of NFIL3 as a new regulator of beige adipocyte reprogramming, systemic energy balance and nutrient homeostasis. Therefore, the successful completion of these studies will lead to the development of new therapeutic approaches for obesity, and other co-morbid metabolic diseases.