FoxM1B Protein in Stimulating Proliferation during Aging

描述（由申请人提供）：衰老过程的潜在机制涉及减少细胞增殖和对组织损伤的修复。这包括DNA复制的减少（s期）和有丝分裂的进展（G2/M阻滞），导致具有4N DNA含量的多倍体细胞的积累，最终导致染色体不稳定和突变，导致老年人中发现的各种疾病。随着年龄的增长，细胞增殖能力逐渐下降的机制尚未明确。最近的研究表明，在衰老过程中，增殖特异性叉头盒M1B （FoxM1B）转录因子的表达减少与细胞增殖和细胞周期进展基因的表达减少有关。我们最近进行了肝脏再生研究，证明在12个月大（老年）转基因（TG）小鼠中维持肝细胞FoxM1B的表达可使肝细胞增殖达到与年轻再生小鼠肝脏相似的水平。在老年增殖细胞中维持FoxM1B水平与进入s期和有丝分裂所需的许多基因的表达增加有关。总之，这些结果表明FoxM1B控制着细胞增殖必需基因的转录网络，其表达的减少有助于衰老过程中细胞增殖的下降。我们的长期目标是确定维持FoxM1B表达是否会防止与年龄相关的增殖缺陷并导致寿命延长。我们计划这样做有以下具体目的：1)我们将有条件地删除年轻成年小鼠的FoxM1B基因，以验证增殖细胞中FoxM1B表达的缺失会导致早衰中观察到的s期和m期进展缺陷的假设。2)我们已经创建了TG小鼠，这些小鼠使用Rosa-26启动子区域来驱动FoxM1B在所有细胞类型中的表达。我们将使用这些小鼠来检验在所有细胞类型中保持FoxM1B水平将在衰老过程中刺激细胞增殖并导致寿命延长的假设。3)我们发现肿瘤抑制蛋白p19ARF （p19）抑制FoxM1B的转录活性。由于FoxM1B控制细胞周期进展基因的表达，这些结果表明p19蛋白也通过抑制FoxM1B转录活性介导生长停滞。我们将进一步表征FoxM1B和p19蛋白的相互作用，并使用来自Rosa26-FoxM1B TG小鼠的小鼠胚胎成纤维细胞（MEFs）来验证FoxM1B水平升高会延迟p19介导的复制性衰老（G1阻滞）的假设。

DESCRIPTION (provided by applicant): An underlying mechanism of the aging process involves reduced cellular proliferation and repair in response to tissue injury. This involves both diminished DNA replication (S-Phase) and progression into mitosis (G2/M block), resulting in accumulation of polyploid cells with 4N DNA content and ultimately causing chromosome instability and mutations leading to a variety of diseases found in the elderly. The mechanisms involved in the progressive decline in cellular proliferation with aging remain uncharacterized. Recent studies have shown that diminished expression of the proliferation-specific Forkhead Box M1B (FoxM1B) transcription factor is associated with reduction in both cellular proliferation and expression of cell cycle progression genes during aging. We recently performed liver regeneration studies to demonstrate that maintaining hepatocyte expression of FoxM1B in 12-month old (old-aged) transgenic (TG) mice increased hepatocyte proliferation to levels similar to those observed in young regenerating mouse liver. Maintaining FoxM1B levels in old-aged proliferating cells is associated with increased expression of numerous genes required for progression into S-phase and mitosis. Collectively, these results suggest that FoxM1B controls the transcriptional network of genes essential for cellular proliferation and that its reduced expression contributes to the decline in cellular proliferation during aging. Our long-term goal is to determine whether maintaining FoxM1B expression will prevent age-related proliferation defects and result in life span extension. We plan to do so with the following Specific Aims: 1) We will conditionally delete the FoxM1B gene in young adult mice to test the hypothesis that extinguished FoxM1B expression in proliferating cells will lead to defective S-phase and M-phase progression observed in premature aging. 2) We have created TG mice that use the Rosa-26 promoter region to drive FoxM1B expression in all cell types. We will use these mice to examine the hypothesis that maintaining FoxM1B levels in all cell types will stimulate cellular proliferation during aging and lead to life span extension. 3) We find that the tumor suppressor protein, p19ARF (p19), inhibits FoxM1B transcriptional activity. Because the FoxM1B controls expression of cell cycle progression genes, these results suggest that the p19 protein also mediates growth arrest by inhibition of FoxM1B transcriptional activity. We will further characterize the FoxM1B and p19 protein interaction and use mouse embryo fibroblasts (MEFs) from Rosa26-FoxM1B TG mice to test the hypothesis that increased FoxM1 B levels will delay p19 mediated replicative senescence (G1 arrest).