TRANSCRIPTIONAL REGULATION OF BEIGE ADIPOCYTE CELLULAR PLASTICITY

肥胖症是美国一个普遍的和日益严重的健康问题，与代谢紊乱有关，包括糖尿病。已经做出了重大努力来通过饮食控制、锻炼或抑制食欲来减轻肥胖。这些方法的成功有限，反弹率很高，因此迫切需要制定新的战略。产热米色脂肪细胞由于其在成年人中的有效抗肥胖活性而作为新的治疗靶点引起了相当大的关注。与保留稳定细胞身份的经典棕色脂肪细胞不同，米色脂肪细胞具有独特的细胞可塑性，能够通过显著的表观基因组重编程在棕色和白色脂肪细胞状态之间完全相互转换。米色脂肪细胞的细胞特性及其潜在的分子机制的非凡的塑料性质还没有得到很好的理解。我们最近的研究导致了一个惊人的发现，定义了米色脂肪细胞的“去分化”潜力。我们发现，在冷暴露后，变白的米色脂肪细胞（米色脂肪细胞变成白色脂肪细胞）的亚群，去分化成祖细胞样细胞，增殖，并可能再分化成产热脂肪细胞。这种重编程过程是米色脂肪细胞募集的一种潜在的新机制。我们的表观基因组分析确定NFIL 3（核因子，白细胞介素3调节）作为一个关键的转录因子，可能介导冷诱导的米色脂肪细胞重编程。NFIL 3表达由冷暴露诱导，特别是在米色但不在棕色脂肪细胞中，并且位于去分化米色脂肪细胞中。此外，体外细胞培养和脂肪细胞中缺乏NFIL 3的体内小鼠模型均证明NFIL 3是冷暴露期间脂肪组织布朗宁所必需的。此外，脂肪细胞中的NFIL 3损失导致高脂肪饮食喂养后对饮食诱导的肥胖症的易感性增加。基于这些数据，我们假设NFIL 3是一个关键的转录因子，通过介导从白色脂肪细胞向棕色脂肪细胞的转变，从而调节能量平衡和葡萄糖稳态，控制米色脂肪细胞的可塑性。在目标1中，我们将阐明在布朗宁过程中变白的米色脂肪细胞的重编程和NFIL 3的作用。我们将使用显微镜、单核RNA-seq和细胞培养在NFIL 3敲除（KO）小鼠中进行米色脂肪细胞脉冲追踪实验。在目标2中，我们将通过对脂肪细胞特异性NFIL 3 KO小鼠进行全面的生理学研究来确定NFIL 3在冷耐受性和葡萄糖稳态中的作用。在目标3中，我们将通过使用ChIP-seq来确定米色脂肪细胞中的NFIL 3顺式组，从而确定NFIL 3调节脂肪细胞身份的分子机制。这些研究将揭示米色脂肪细胞可塑性的新方面。我们将确定NFIL 3作为米色脂肪细胞重编程、全身能量平衡和营养稳态的新调节剂的作用。因此，这些研究的成功完成将导致肥胖症和其他共病代谢疾病的新治疗方法的开发。

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.