The role of p16INK4a in mammalian aging

描述(由申请人提供)：有人建议，某些肿瘤抑制机制的有益抗癌功能，如衰老，可能会不知不觉地导致衰老。在这个模型中，预防癌症的基因也会限制组织的再生和修复，从而损害机体的健康。一些证据表明，肿瘤抑制基因p16INK4a是衰老的有力媒介，是这种衰老分子效应的有力候选者。首先，缺乏p16INK4a的小鼠容易患肿瘤，但在其他方面发育正常；这表明p16INK4a在体内的主要功能是消除肿瘤。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著的p16INK4a表达，但在老年哺乳动物中广泛表达。由于p16INK4a唯一已知的功能是诱导细胞周期停滞，这种增加的p16INK4a表达可能在衰老所特有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-/-小鼠表现出与年龄相关的T细胞和胰岛功能的生理性衰退的缓解。特别是，后一种表型可增强成年p16INK4a-/-小鼠的葡萄糖耐量和对胰岛细胞毒素的抵抗力。在特定的目的I中，我们建议通过实时荧光定量聚合酶链式反应、免疫组织化学和RNA原位方法，对p16INK4a在年轻和老年小鼠的几个组织中的表达进行严格的表征。 这些数据将为特定目标II提供信息，在该目标中，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、衰老等)。在缺乏p16INK4a的小鼠中与正常仔鼠对照。在这些实验中，我们将p16INK4a缺陷的动物回交到同质和更具抗肿瘤能力的遗传背景(C57BL/6)，以便在较年长的p16INK4a-/-小鼠中进行研究。在特定目的III中，我们将寻求通过产生在其内源启动子控制下过表达p16INK4a的低拷贝数BAC转基因小鼠来提供p16INK4a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特定目标II的方式进行表征。通过这些方法，我们将检测p16INK4a表达的体内组织和年龄特异性的影响，并描绘其对多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.