TRANSCRIPTIONAL REGULATION OF BEIGE ADIPOCYTE CELLULAR PLASTICITY

在美国，肥胖是一个普遍且日益严重的健康问题，与包括糖尿病在内的代谢紊乱有关。已经做出了重大努力，通过控制饮食、锻炼或抑制食欲来减轻肥胖。这些方法都取得了有限的成功，但反弹的几率很高，因此迫切需要开发新的策略。生热米色脂肪细胞作为一种新的治疗靶点已经引起了相当大的关注，因为它们在成人中具有强大的抗肥胖活性。与保持稳定细胞特性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新编程在棕色和白色脂肪细胞状态之间完全相互转换。米色脂肪细胞的特殊可塑性细胞特性及其潜在的分子机制尚未被很好地理解。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”潜能。我们发现冷暴露后，白化的米色脂肪细胞亚群(米色脂肪细胞转变为白色脂肪细胞)，去分化为祖细胞样细胞，增殖，并可能重新分化为产热脂肪细胞。这种重新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NFIL3(核因子，白介素3调节)是一个关键的转录因子，可能介导冷诱导的米色脂肪细胞重新编程。冷暴露诱导NFIL3的表达，在米色脂肪细胞中表达，但在棕色脂肪细胞中不表达，定位于去分化的米色脂肪细胞。此外，体外细胞培养和体内脂肪细胞中NFIL3缺失的小鼠模型都表明，NFIL3是冷暴露下脂肪组织褐变所必需的。此外，脂肪细胞中NFIL3的丢失导致高脂饮食喂养后饮食诱导肥胖的易感性增加。根据这些数据，我们推测NFIL3是一个关键的转录因子，通过介导脂肪细胞从白色到棕色的转变来控制米色脂肪细胞的可塑性，从而调节能量平衡和葡萄糖稳态。在目标1中，我们将阐明变白的米色脂肪细胞在褐化过程中的重新编程以及NFIL3的作用。我们将在NFIL3基因敲除(KO)小鼠中进行米色脂肪细胞脉冲追逐实验，使用显微镜、单核RNA-SEQ和细胞培养。在目标2中，我们将通过对脂肪细胞特异的NFIL3 KO小鼠进行全面的生理学研究，来确定NFIL3在耐寒和血糖动态平衡中的作用。在目标3中，我们将通过使用CHIP-SEQ定义米色脂肪细胞中的NFIL3周期来确定NFIL3调节脂肪细胞特性的分子机制。这些研究将揭示米色脂肪细胞细胞可塑性的新方面。我们将确定NFIL3作为米色脂肪细胞重新编程、全身能量平衡和营养动态平衡的新调节器的作用。因此，这些研究的成功完成将导致开发治疗肥胖症和其他共病代谢性疾病的新方法。

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.