The role of p16INK4a in mammalian aging

描述（由申请人提供）：已表明某些肿瘤抑制机制（如衰老）的有益抗癌功能可能会导致衰老。在这个模型中，预防癌症的基因也通过限制组织再生和修复来损害生物体的适应性。一些证据表明，肿瘤抑制因子p16 INK 4a是一种有效的衰老介质，是这种衰老分子效应器的有力候选者。首先，缺乏p16 INK 4a的小鼠有肿瘤倾向，但在其他方面发育正常;这表明p16 INK 4a在体内的主要功能是消除肿瘤形成。此外，我们和其他人已经表明，在年轻的啮齿动物和人类中没有检测到显着的p16 INK 4a表达，但在老年哺乳动物中广泛表达。由于p16 INK 4a的唯一已知功能是诱导细胞周期停滞，这种增加的p16 INK 4a表达可能在衰老的组织再生和干细胞功能特征受损中起重要作用。为了支持这一假设，我们最近对p16 INK 4a-/-动物的研究数据表明，缺乏p16 INK 4a的小鼠对某些衰老表型具有抵抗力。例如，p16 INK 4a-/-小鼠表现出与生理年龄相关的T细胞和胰岛功能下降的减弱。特别是，后一种表型在成年p16 INK 4a-/-小鼠中产生增强的葡萄糖耐量和对胰岛细胞毒素的抗性。在具体目标I中，我们建议通过实时PCR、免疫组织化学和RNA原位方法，严格表征p16 INK 4a在年轻和老年小鼠的几个组织隔室中的表达。 这些数据将为具体目标II提供信息，我们计划进一步研究几种衰老表型（例如长寿、葡萄糖耐量、造血干细胞功能、免疫功能、骨密度、伤口愈合、变灰等）。在缺乏p16 INK 4a的小鼠中与正常同窝对照相比。对于这些实验，我们将p16 INK 4a缺陷动物与同质且更具肿瘤抗性的遗传背景（C57 Bl/6）回交，从而允许研究年龄较大的p16 INK 4a-/-小鼠。在具体目标III中，我们将寻求通过产生在其内源性启动子控制下过表达p16 INK 4a的低拷贝数BAC转基因小鼠来提供p16 INK 4a表达有助于衰老的遗传学证实。这些动物的衰老表型将以类似于具体目标II的方式进行表征。通过这些方法，我们将研究p16 INK 4a表达的体内组织和年龄特异性效应，并描述其对各种哺乳动物衰老表型的贡献。

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.