The Role of p16INK4 in Mammalian Aging

 描述(申请人提供)：我们实验室和其他实验室的工作已经证实，p16INK4a肿瘤抑制机制的表达在哺乳动物衰老中起着关键作用。P16INK4a在某些细胞应激和组织病理环境中的表达显然在限制与过度增殖相关的重要年龄相关疾病方面发挥了有益的作用，如癌症和动脉粥样硬化。然而，p16INK4a在整个生命过程中的激活与经历了衰老的细胞的积累有关，衰老是一种永久性的生长停滞形式，这也与致病的、促炎的细胞因子的形成有关。因此，p16INK4a有益的防癌表达通过限制某些自我更新的隔间的再生和修复，损害了机体随年龄增长的某些方面的健康。在这项提议的前十年中，我们的团队及其合作者为这一模型提供了重要的证据。2004年，我们发现p16INK4a是哺乳动物衰老的可靠生物标志物。2006年，我们发现p16INK4a缺乏的动物表现出对胰腺细胞、神经干细胞和造血干细胞中某些衰老表型的抵抗，而表达过量p16INK4a的转基因动物随着年龄的增长表现出加速的功能衰退。2009年，我们开发了一种方法来测量p16INK4a在人类中随年龄增长的表达，并使用这种方法来显示吸烟、缺乏体育锻炼、慢性艾滋病毒感染和细胞毒性化疗对人的衰老促进作用。我们还发现了一种在人类中非常常见的多态性，它强烈影响p16INK4a的表达，并与动脉粥样硬化性疾病相关。2011年，我们展示了p16INK4a表达在衰老的B-淋巴细胞和T-淋巴细胞的生理学中的重要作用，并解释了p16INK4a表达如何限制动脉粥样硬化性疾病。最后，我们在2013年的《细胞》杂志上报道，p16INK4a的表达随着年龄的增长并不能预测小鼠的恶性肿瘤风险，并表明基因座的激活在体内是通过细胞非自主机制产生的。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p16INK4a如何影响哺乳动物衰老的理解。在特定目的I中，我们利用新的报告基因和p16CRE等位基因来研究表达p16INK4a的细胞在体内是否总是衰老。在特定的目标II中，我们将使用遗传学或免疫方法来研究耗尽p16INK4a表达的细胞在肿瘤发生和衰老中的作用。在特定的目标III中，我们将研究细胞表观遗传状态的变化对p16INK4a表达和随年龄增长的体细胞干细胞功能的影响。通过这些途径，我们将进一步阐明p16INK4a的表达和细胞衰老在哺乳动物衰老中的作用。

 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.