The Role of p16INK4 in Mammalian Aging

 描述（由申请人提供）：我们实验室和其他人的工作已经确定，p16 INK 4a肿瘤抑制机制的表达在哺乳动物衰老中起着关键作用。p16 INK 4a在某些细胞应激和组织病理学环境中的表达在限制与过度增殖相关的重要年龄相关疾病如癌症和动脉粥样硬化方面明显发挥有益作用。然而，在整个生命过程中p16 INK 4a的激活与已经经历衰老的细胞的积累有关，这是一种永久性的生长停滞形式，也与致病性促炎细胞因子的产生有关。因此，p16 INK 4a的有益的癌症预防表达通过限制某些自我更新区室的再生和修复而损害了生物体适应性的某些方面。在提出这一建议的前十年中，我们的小组与合作者一起为这一模型提供了重要的证据。2004年，我们发现p16 INK 4a是哺乳动物衰老的可靠生物标志物。在2006年，我们发现p16 INK 4a缺陷动物在胰腺干细胞、神经干细胞和造血干细胞中表现出对某些衰老表型的抵抗，而表达过量p16 INK 4a的转基因动物在这些隔室中表现出随着衰老的加速功能衰退。2009年，我们开发了一种方法来测量p16 INK 4a表达与人类衰老，并采用这种方法来显示烟草使用，身体活动不足，慢性HIV感染和细胞毒性化疗对人的年龄促进作用。我们还发现了人类中一种非常常见的多态性，它强烈影响p16 INK 4a的表达，并与动脉粥样硬化疾病相关。在2011年，我们发现p16 INK 4a表达对衰老B-与T-淋巴细胞的生理学有重要影响，并解释了p16 INK 4a表达如何限制动脉粥样硬化疾病。最后，在2013年，我们在Cell上报道了p16 INK 4a表达与衰老并不能预测小鼠的恶性肿瘤风险，并表明基因座激活是由细胞非自主机制引起的体内结果。在更新这一建议时，我们试图扩展这些先前的观察结果，以进一步增强我们对p16 INK 4a如何影响哺乳动物衰老的理解。在具体目标I中，我们采用新的报告基因和p16 CRE等位基因来研究表达p16 INK 4a的细胞是否总是在体内衰老。在具体目标II中，我们将使用遗传或免疫方法研究耗尽p16 INK 4a表达细胞对肿瘤发生和衰老的影响。在具体目标III中，我们将研究细胞表观遗传状态的改变对p16 INK 4a表达和衰老过程中体干细胞功能的影响。通过这些方法，我们将进一步阐明p16 INK 4a表达和细胞衰老对哺乳动物衰老的贡献。

 DESCRIPTION (provided by applicant): Work from our lab and others has established that expression of the p16INK4a tumor suppressor mechanism plays a critical role in mammalian aging. The expression of p16INK4a in the setting of certain cellular stresses and tissue pathology clearly plays a beneficial role in limiting important age-associated conditions associated with excess proliferation such as cancer and atherosclerosis. The activation of p16INK4a throughout life, however, is associated with the accumulation of cells that have undergone senescence, a permanent form of growth arrest, which is also associated with the elaboration of pathogenic, pro-inflammatory cytokines. Therefore, the beneficial cancer-preventing expression of p16INK4a compromises some aspects of organismal fitness with aging by limiting the regeneration and repair of certain self-renewing compartments. During the prior ten years of this proposal, our group, with collaborators, has provided significant evidence for this model. In 2004, we showed that p16INK4a is a faithful biomarker of mammalian aging. In 2006, we showed that p16INK4a-deficient animals demonstrate a resistance to some aging phenotypes in pancreatic ß-cells, neural stem cells and hematopoietic stem cells, while transgenic animals expressing excess p16INK4a demonstrate an accelerated functional decline with aging in these compartments. In 2009, we developed an approach to measuring p16INK4a expression with aging in humans, and employed this assay to show the age-promoting effects of tobacco use, physical inactivity, chronic HIV infection, and cytotoxic chemotherapy in people. We also identified a highly common polymorphism in humans that strongly affects p16INK4a expression and is associated with atherosclerotic disease. In 2011, we showed an important effect of p16INK4a expression on the physiology of aging B- vs. T-lymphocytes, and provided an explanation for how p16INK4a expression limits atherosclerotic disease. Finally, in 2013, we reported in Cell that p16INK4a expression with aging does not predict malignancy risk in mice, and showed that locus activation results in vivo from cell-non-autonomous mechanisms. In the renewal of this proposal, we seek to extend these prior observations to further enhance our understanding of how p16INK4a influences mammalian aging. In specific aim I, we employ novel reporter and p16CRE alleles to study whether p16INK4a expressing cells are always senescent in vivo. In specific aim II, we will examine the effects of depleting p16INK4a-expressing cells on tumorigenesis and aging using a genetic or immune approach. In specific aim III, we will examine the effects of alterations in the cellular epigenetic state on expression f p16INK4a and somatic stem cell function with aging. Through these approaches, we will further delineate the contribution of p16INK4a expression and cellular senescence to mammalian aging.