Regulation of adult pancreatic beta cell replication

描述(由申请人提供)： 2型糖尿病和妊娠期糖尿病的发病率都随着年龄的增长而增加，部分原因是随着个体年龄的增长，b细胞的增殖能力下降。这可能部分是由于衰老的b细胞中细胞周期抑制物的表达增加，而伴随而来的是细胞周期激活物的表达减少。然而，胰岛素抵抗状态，如肥胖和怀孕，通常会刺激成人静止的b细胞复制。面对胰岛素抵抗，未能增加b细胞质量可能会导致2型糖尿病或妊娠期糖尿病。FOXM1转录因子在增殖细胞中表达，调节细胞周期基因，促进细胞周期进程。甘农实验室发现，胰腺中缺乏foxm1的小鼠在四周大后由于b细胞团扩增失败而患上糖尿病。我们随后发现FOXM1对于b细胞复制是必不可少的，以响应所有测试的刺激，包括胰腺损伤、怀孕和高脂肪饮食。在体内，B细胞增殖刺激均可诱导FOXM1基因表达。我们假设FOXM1代表所有刺激b细胞增殖的途径相交的结点，并且FOXM1的基因表达和蛋白活性被b细胞增殖刺激增强。我们预测FOXM1是增强老年b细胞复制的极佳候选基因，因此可能成为改善糖尿病患者b细胞质量的靶点。这些假说将通过体外和体内方法进行检验。在体外，我们将确定已知的b细胞增殖第二信使信号通路的药理激活剂是否诱导不同年龄小鼠分离的胰岛FOXM1基因表达和/或蛋白活性。在体内，我们将使用微阵列分析来确定在正常和刺激条件下FOXM1缺失对b细胞转录组的影响。我们还将研究FOXM1是否主要通过抑制细胞周期抑制物来促进b细胞复制。最后，我们将测试在老化的b细胞中表达一种激活形式的FOXM1是否能够克服通常随着年龄增长而出现的复制下降。对FOXM1如何调节b细胞复制的透彻了解将导致促进b细胞增殖和增加b细胞质量的策略，用于治疗糖尿病，糖尿病目前影响16%的退伍军人人口，预计在未来几年将进一步增加。 公共卫生相关性： 有几个信号通路激活了b细胞的复制；然而，b细胞对这些信号的反应能力随着年龄的增长而降低。我们将确定在不同年龄分离的胰岛中，哪些信号通路最有力地诱导关键细胞周期转录因子FOXM1的表达和活性。这些研究还将确定FOXM1在复制b细胞时调节哪些下游靶基因，以及激活的FOXM1是否可以克服年龄相关的b细胞增殖障碍。糖尿病随着年龄的增长而增加，b细胞的复制随着年龄的增长而下降。因此，随着退伍军人的老龄化，糖尿病将变得更加普遍。拟议的研究将确定FOXM1的激活是否代表一个潜在的干预目标。

DESCRIPTION (provided by applicant): The incidence of both Type 2 and gestational diabetes increase with age, due in part to a decline in b cell proliferation as individuals age. This may be due in part to the increased expression of cell cycle inhibitors in aged b cells, and a concomitant decrease in expression of cell cycle activators. However, insulin resistant states, such as obesity and pregnancy, normally stimulate replication in adult quiescent b cells. Failure to increase b cell mass in the face of insulin resistance can lead to Type 2 diabetes or gestational diabetes. The FoxM1 transcription factor is expressed in proliferating cells, regulates cell cycle genes, and promotes cell cycle progression. The Gannon lab discovered that mice lacking FoxM1 in their pancreas became diabetic due to a failure of b cell mass expansion after four weeks of age. We subsequently showed that FoxM1 is essential for b cell replication in response to all stimuli tested including pancreatic injury, pregnancy, and high fat diet. b cell proliferative stimuli were all found to induce Foxm1 gene expression in vivo. We hypothesize that FoxM1 represents a nodal point at which all stimulatory pathways for b cell proliferation intersect, and that FoxM1 gene expression and protein activity are enhanced by b cell proliferative stimuli. We predict that FoxM1 represent an excellent candidate for enhancement of replication in older b cells and thus may be a target for improving b cell mass expansion in diabetic individuals. These hypotheses will be tested using in vitro and in vivo approaches. In vitro, we will determine whether pharmacological activators of known b cell proliferative second messenger signaling pathways induce Foxm1 gene expression and/or protein activity in islets isolated from mice of different ages. In vivo, we will use microarray analyses to determine the effects of loss of FoxM1 on the b cell transcriptome under normal and stimulatory conditions. We will also examine whether FoxM1 mainly acts to promote b cell replication through its repression of cell cycle inhibitors. Finally, we will test whether expression of an activated form of FoxM1 in aged b cells is able to overcome the decline in replication that normally occurs with age. A thorough understanding of how FoxM1 functions to regulate b cell replication will lead to strategies for enhancing b cell proliferation and augmenting b cell mass for the treatment of diabetes, a disease that currently affects 16% of the veteran population and is expected in to increase even further in the coming years. PUBLIC HEALTH RELEVANCE: Several signaling pathways activate b cell replication; however, the ability of b cells to respond to these signals decreases with age. We will determine which signaling pathways most robustly induce expression and activity of the critical cell cycle transcription factor, FoxM1, in islets isolated at different ages. These studies will also determine what downstream target genes FoxM1 regulates in replicating b cells and whether activated FoxM1 can overcome age-dependent blocks to b cell proliferation. Diabetes increases with age and b cell replication declines with age. Thus, as the veteran population ages, diabetes will become more prevalent. The proposed studies will determine whether activation of FoxM1 represents a potential target for intervention.