Age-related Responses of Epidermal Stem Cells to Environ

持续更新的组织（如表皮）的稳态由体干细胞维持。 这些是未分化的自我更新细胞，也产生子瞬时扩增（TA）细胞，构成增殖群体的大部分。 TA细胞在离开增殖区室并向终末分化移动之前经历有限数量的细胞分裂，而已经假设干细胞在生物体的整个寿命中持续存在。 通过一系列的标记实验与氚标记的胸苷，我们以前表明，干细胞从成年小鼠皮肤不分裂，因为经常作为其他基底细胞，但他们在体内以稳定的速度分裂。 我们还表明，它们在整个生命过程中继续在体内增殖，并且它们在体外具有高增殖潜力。 因此，表皮干细胞可能不遵循海弗利克理论，可能“永生”。“去年，我们开发了一种分选方法，可以从表皮中产生一个可行的干细胞群。 我们发现，这些干细胞具有再生表皮的能力，并在再生组织中持续表达重组基因。 因此，它们是表皮的干细胞。 最近，我们确定这些表皮干细胞也具有参与其他组织形成的显著能力，其可塑性类似于胚胎干细胞和其他一些体干细胞。 我们的初步数据显示，从新生小鼠皮肤中分离的表皮干细胞在注射到囊胚中后可整合到多种组织中并改变其表型。 因此，这些干细胞的命运决定似乎是对其环境的直接反应。 我们还确定，这些细胞的细胞周期谱似乎是干细胞的内在特性，与细胞的年龄无关。 这些数据让我们不禁要问，随着机体衰老，表皮干细胞会发生什么变化？ 在本申请中，我们建议测试干细胞的年龄是否对其对环境或外在因素的反应有影响，以确定其命运途径。 我们提出了以下具体目标：1）通过测定注射到胚泡中后的老年与年轻小鼠表皮干细胞的数量、改变的表型和寿命来比较老年与年轻小鼠表皮干细胞，并确定注射老年与年轻干细胞的胚泡衍生的小鼠的寿命是否存在差异;和2）通过确定老年人表皮干细胞与年轻人表皮干细胞的体外生长潜力是否存在差异以及它们在体外和注射到胚泡中后对外部环境信号的反应是否不同来比较老年人表皮干细胞与年轻人表皮干细胞。

Homeostasis of continuously renewing tissues, such as the epidermis, is maintained by somatic stem cells. These are undifferentiated, self-renewing cells, which also produce daughter transient amplifying (TA) cells that make up the majority of the proliferative population. TA cells undergo a finite number of cell divisions before leaving the proliferative compartment and moving toward terminal differentiation, whereas it has been assumed that the stem cells persist throughout the lifetime of the organism. Through a series of labeling experiments with tritiated thymidine, we previously showed that stem cells from adult mouse skin did not divide as often as the other basal cells, but they did divide at a steady rate in vivo. We also showed that they continued to proliferate in vivo throughout life, and that they have a high proliferative potential in vitro. Thus, it may be that epidermal stem cells do not follow the Hayflick theory and possibly "live forever." Last year, we developed a sorting method that yields a viable population of stem cells from the epidermis. We showed that these stem cells have the capacity to regenerate the epidermis and to continuously express a recombinant gene in the regenerated tissue. Thus, they are the stem cells for the epidermis. Very recently, we determined that these epidermal stem cells also have the remarkable ability to participate in the formation of the other tissues, a plasticity similar to that of embryonic stem cells and a few other somatic stem cells. Our preliminary data show that the epidermal stem cells isolated from neonatal mouse skin incorporate into a variety of tissues and alter their phenotype after injection into blastocysts. Thus, the fate determination of these stem cells appears to be in direct response to their environment. We also determined that the cell cycle profile of these cells appears to be an intrinsic property of the stem cell and not related to the age of the cell. These data have led us to ask what happens to epidermal stem cells as the organism ages? In this application, we propose to test whether the age of the stem cells has an effect on its response to the environment or extrinsic factors in determining its fate pathway. We propose the following specific aims: 1) to compare old vs. young murine epidermal stem cells by determining their number, altered phenotype and longevity after injection into blastocysts, and to determine whether there is a difference in the life span of mice derived from blastocysts injected with old vs. young stem cells; and 2) to compare old vs. young adult human epidermal stem cells by determining if there is a difference in their in vitro growth potential and if they respond differently to extrinsic environmental signals in vitro and after injection into blastocysts.