The role of p16INK4a in mammalian aging

描述（由申请人提供）：有人认为某些肿瘤抑制机制（如衰老）的有益抗癌功能可能会导致衰老。在这个模型中，预防癌症的基因也会通过限制组织再生和修复来损害有机体的健康。一些证据表明，肿瘤抑制因子p16INK4a是一种有效的衰老介质，是这种衰老分子效应的有力候选者。首先，缺乏p16INK4a的小鼠易患肿瘤，但其他方面发育正常；提示p16INK4a在体内的主要功能是消除肿瘤。此外，我们和其他人已经证明p16INK4a在幼年啮齿动物和人类中未检测到显著表达，但在老年哺乳动物中广泛表达。由于p16INK4a已知的唯一功能是诱导细胞周期阻滞，p16INK4a表达的增加可能在衰老的组织再生和干细胞功能受损中发挥重要作用。为了支持这一假设，我们最近对p16INK4a-/-动物的研究数据表明，缺乏p16INK4a的小鼠对某些衰老表型具有抵抗力。例如，p16INK4a-/-小鼠表现出t细胞和胰岛功能与年龄相关的生理性衰退的衰减。特别是，后一种表型在成年p16INK4a -/-小鼠中产生增强的葡萄糖耐量和对胰岛细胞毒素的抗性。在具体的目的1中，我们提出通过实时PCR、免疫组织化学和RNA原位方法严格表征p16INK4a在年轻和老年小鼠几个组织室中的表达。

DESCRIPTION (provided by applicant): It has been suggested that the beneficial, anti-cancer functions of certain tumor suppressor mechanisms such as senescence may untowardly contribute to aging. In this model, genes that prevent cancer also compromise organismal fitness by limiting tissue regeneration and repair. Several lines of evidence suggest the tumor suppressor p16INK4a, a potent mediator of senescence, is a strong candidate for such a molecular effector of aging. First, mice lacking p16INK4a are tumor prone but otherwise developmentally normal; suggesting p16INK4a is majorin vivo function is to abrogate neoplasia. Additionally, we and others have shown that significant p16INK4a expression is not detected in young rodents and humans, yet is widely expressed in older mammals. As the only known function of p16INK4a is to induce cell cycle arrest, this increased p16 INK4a expression may play a significant role in the impaired tissue regeneration and stem cell function characteristic of aging. In support of this hypothesis, our recent data from the study of p16INK4a-/- animals demonstrates that mice lacking p16 INK4a possess a resistance to certain aging phenotypes. For example, p16INK4a-/- mice demonstrate attenuation of the physiologic age-associated decline of function of T-cells and pancreatic islets. In particular, this latter phenotype produces enhanced glucose tolerance and resistance to an islet cell toxin in adult p16INK4a -/- mice. In specific aim I, we propose to characterize rigorously the expression of p16INK4a in several tissue compartments in young and aged mice through real-time PCR, immunohistochemical and RNA in situ approaches. This data will inform specific aim II, in which we plan to study further several aging phenotypes (e.g. longevity, glucose tolerance, hematopoetic stem cell function, immune function, bone density, wound healing, graying, etc.) in mice lacking p 16INK4a compared to normal littermate controls. For these experiments, we have backcrossed p16INK4a deficient animals to a homogeneous and more tumor-resistant genetic background (C57Bl/6), allowing for the study of p16INK4a -/- mice at older ages. In specific aim III, we will seek to provide genetic confirmation that p16INK4a expression contributes to aging through the generation of low copy-number BAC transgenic mice that over-express p16INK4a under the control of its endogenous promoter. The aging phenotypes of these animals will be characterized in a way analogous to specific aim II. Through these approaches, we will examine the in vivo tissue and age-specific effects of p16INK4a expression, and delineate its contribution to a variety of mammalian aging phenotypes.