The Regulation of Stem Cell Aging

正如我们在进度报告中详细描述的那样，过去三年的供资产生的数据 证明存在异时基因产物网络，包括let-7 microRNA，IMP 1，Hmga 2， P16 lnk 4a和可能的p19 Arf，调节整个生命过程中干细胞功能的时间变化，包括 干细胞衰老在下一个五年的资助期内，我们建议扩大我们对这方面的认识 通过探索在衰老过程中调节P16 lnk 4a/p19 Arf表达增加的新机制来研究P16 lnk 4a/p19 Arf网络。 P16 lnk 4 a是一种细胞周期蛋白依赖性激酶抑制剂，与替代阅读框架（Alternative Reading Frame，Arf）位于同一位点 编码p19 Arf肿瘤抑制因子。已知P16 lnk 4a/p19 Arf表达在小鼠中随年龄增加， 它被认为是衰老的生物标志物。P16 lnk 4a表达的增加有助于细胞凋亡。 干/祖细胞功能在多种衰老组织中的下降，我们目前正在测试 p19 Arf表达的增加也降低了神经干/祖细胞的功能， 老化组织的能力。在衰老过程中调节P16 lnk 4a/p19 Arf表达的机制是感兴趣的， 扩大我们对异时基因网络及其在干细胞衰老中的作用的理解。我们有 先前表明，polycomb复合物1组分Bmi-1在出生后早期是必需的 通过负调控P16 lnk 4a/p19 Arf表达来维持前脑干细胞功能。类似 机制促进干细胞在其他组织中的维持。然而，一个主要的限制是， 无法测试Bmi-1是否调节成体干细胞功能或衰老。迄今为止发表的所有研究 对干细胞中Bmi-1功能的研究已经在生殖系敲除小鼠中进行，这些小鼠在两个月后死亡， 年龄为了测试Bmi-1是否调节成体干细胞功能、干细胞老化以及Bmi-1基因的增加， 在衰老过程中P16 lnk 4a/p19 Arf的表达我们已经产生了携带Bmi-1的floxed等位基因的小鼠。在 未发表的初步研究发现，从成人神经干/祖细胞中条件性缺失Bmi-1， 细胞导致前脑干/祖细胞功能和神经发生过早下降， P16 lnk 4a/p19 Arf表达显著增加。P16 lnk 4a/p19 Arf的增加幅度 随着年龄的增长，Bmi-1的表达量急剧上升，这表明Bmi-1通过对抗干细胞衰老， P16 lnk 4a/p19 Arf表达增加。我们的数据还显示，需要Bmi-1来预防年龄相关的 运动功能和平衡方面的行为缺陷，与本体感觉和 白内障的过早发展。我们建议测试是否需要Bmi-1来预防早产儿 干细胞衰老和神经缺陷的发展，通过对抗与年龄相关的增加， P16 lnk 4a/p19 Arf表达。

As described in detail in our progress report, the data generated over the past three years of funding demonstrate there is a network of heterochronic gene products, including let-7 microRNAs, IMP1, Hmga2, P16lnk4a and possibly p19Arf, that regulates temporal changes in stem cell function throughout life, including stem cell aging. During the next five-year funding period we propose to expand our understanding of this network by exploring new mechanisms that regulate the increase in P16lnk4a/p19Arf expression during aging. P16lnk4a is a cyclin-dependent kinase inhibitor and the Alternative Reading Frame (Arf) at the same locus encodes the p19Arf tumor suppressor. P16lnk4a/p19Arf expression is known to increase with age in mice and humans and is considered a biomarker of aging. The increase in P16lnk4a expression contributes to the decline in stem/progenitor cell function in multiple aging tissues and we are currently testing whether the increase in p19Arf expression also decreases neural stem/progenitor cell function and the regenerative capacity of aging tissues. Mechanisms that regulate P16lnk4a/p19Arf expression during aging are of interest to expand our understanding of the heterochronic gene network and its role in stem cell aging. We have shown previously that the polycomb complex 1 component, Bmi-1, is required in the early postnatal period to maintain forebrain stem cell function by negatively regulating P16lnk4a/p19Arf expression. Similar mechanisms promote stem cell maintenance in other tissues. However, a major limitation has been the inability to test whether Bmi-1 regulates adult stem cell function or aging. All of the studies published so far on Bmi-1 function in stem cells have been performed with germline knockout mice that die by two months of age. To test whether Bmi-1 regulates adult stem cell function, stem cell aging, and the increase in P16lnk4a/p19Arf expression during aging we have generated mice bearing a floxed allele of Bmi-i. In unpublished preliminary studies we find that conditional deletion of Bmi-1 from adult neural stem/progenitor cells leads to premature declines in forebrain stem/progenitor cell function and neurogenesis as well as a profound age-related increase in P16lnk4a/p19Arf expression. The magnitude of the increase in P16lnk4a/p19Arf expression climbed sharply with age, suggesting that Bmi-1 delays stem cell aging by opposing the increase in P16lnk4a/p19Arf expression. Our data also revealed requirements for Bmi-1 to prevent age-related behavioral deficits in motor function and balance that are associated with defects in proprioception and the premature development of cataracts. We propose to test whether Bmi-1 is required to prevent premature stem cell aging and the development of neurological deficits by opposing the age-related increase in P16lnk4a/p19Arf expression.