Cell cycle control of adipogenesis

最近的证据表明，创造新的脂肪细胞(脂肪生成)可以抵消 肥胖的有害代谢影响，已被证明主要源于异常 现有脂肪细胞的肥大(肥大)和由此导致的功能障碍。由此可见，如何增加 脂肪生成超过肥大是人们非常感兴趣的问题。先前的研究表明，体内的前脂肪细胞 体内和体外必须完成一个或多个细胞周期，这一过程被称为克隆扩增， 才能分化成脂肪细胞。最引人注目的遗传例子之一 通过控制这一克隆扩张期可以增加脂肪生成。 敲除细胞周期抑制因子p21和p27。小鼠p21或p27基因敲除结果 脂肪生成和脂肪质量增加2倍，但同时剔除这两种基因会导致显著增加6倍 增加。以前的工作表明，p21和p27是由非常不同的机制和 在脂肪生成的不同时间都是活跃的。在最近出版的著作中，我们确定了 可以解释p21-2中脂肪生成增加的分子机制 基因敲除老鼠。然而，p27如何调控脂肪生成和组织质量，以及p21和p27如何 人们对协同作用知之甚少。我们假设p21和p27的协同表达 在脂肪形成过程中是控制细胞分裂数量的主要机制 分化，从而控制每个前脂肪细胞产生的脂肪细胞的数量。我们会 通过使用活细胞成像方法来验证这一假设。我们将首先使用归纳的方法 表达并快速降解p27以确定p27何时以及如何调节细胞周期进程 在成脂过程中。然后我们将使用CDK4/6和CDK2活性的活细胞记者来 了解p27和p21何时以及如何协同调节CDK4/6和CDK2活性 控制产生的脂肪细胞的数量。最后，我们将使用实况细胞记者和p27 基因敲除细胞和小鼠模型，以了解p27是如何受上游细胞密度和 细胞外基质僵硬信号在脂肪形成过程中打开和关闭增殖窗口。 这项工作的结果将是一个如何控制克隆扩张期的框架 显著增加脂肪生成而不是肥大，同时还确保祖细胞 池得到维护。我们的结果可能不仅对维护具有广泛的适用性 脂肪组织，但更普遍的是维持和再生神经元，肌肉， 和其他终末分化组织。

Recent evidence shows that creating new fat cells (adipogenesis) can counteract the harmful metabolic effects of obesity, which have been shown to originate primarily from abnormal enlargement (hypertrophy) and resulting dysfunction of existing fat cells. Thus, how to increase adipogenesis over hypertrophy is of great interest. Previous work showed that preadipocytes in vivo and in vitro must complete one or more cell cycles, a process referred to as clonal expansion, before they can differentiate into adipocytes. One of the most striking genetic examples of increased adipogenesis was demonstrated by manipulating this clonal expansion period by knocking out the cell cycle inhibitors p21 and p27. Knockout of either p21 or p27 in mice results in a 2-fold increase in adipogenesis and fat mass, but knockout of both results in a dramatic 6-fold increase. Previous work suggests that p21 and p27 are regulated by very different mechanisms and are active at different times during adipogenesis. In recent published work, we identified the molecular mechanisms that could explain the increased adipogenesis observed in the p21- knockout mouse. However, how p27 regulates adipogenesis and tissue mass and how p21 and p27 synergize are poorly understood. We hypothesize that the synergistic expression of p21 and p27 during adipogenesis is the primary mechanism that controls the number of cell divisions before differentiation, and thus controls the number the adipocytes produced per preadipocyte. We will test this hypothesis by using live-cell imaging approaches. We will first use methods to inducibly express and rapidly degrade p27 to determine when and how p27 regulates cell cycle progression during adipogenesis. We will then use live cell reporters for CDK4/6 and CDK2 activity to understand when and how p27 and p21 synergize to regulate CDK4/6 and CDK2 activity and control the number of adipocytes produced. Finally, we will use live-cell reporters and p27 knockout cell and mouse models to understand how p27 is regulated by upstream cell density and extracellular matrix stiffness signals to open and close a proliferative window during adipogenesis. The outcome of this work will be a framework how the clonal expansion period can be controlled to significantly increase adipogenesis over hypertrophy while also ensuring that the progenitor pool is maintained. Our results will likely have broad applicability not only to the maintenance of adipose tissue, but also more generally for the maintenance and regeneration of neuronal, muscle, and other terminally differentiated tissues.