Randall T D, Weissman I L
Department of Pathology, Stanford Medical School, CA 94305, USA.
Blood. 1997 May 15;89(10):3596-606.
A significant fraction of hematopoietic stem cells (HSCs) have been shown to be resistant to the effects of cytotoxic agents such as 5-fluorouracil (5-FU), which is thought to eliminate many of the rapidly dividing, more committed progenitors in the bone marrow and to provide a relatively enriched population of the most primitive hematopoietic progenitor cells. Although differences between 5-FU-enriched progenitor populations and those from normal bone marrow have been described, it remained unclear if these differences reflected characteristics of the most primitive stem cells that were revealed by 5-FU, or if there were changes in the stem-cell population itself. Here, we have examined some of the properties of the stem cells in the bone marrow before and after 5-FU treatment and have defined several activation-related changes in the stem-cell population. We found that long-term reconstituting stem cells decrease their expression of the growth factor receptor c-kit by 10-fold and increase their expression of the integrin Mac-1 (CD11b). These changes begin as early as 24 hours after 5-FU treatment and are most pronounced within 2 to 3 days. This activated phenotype of HSCs isolated from 5-FU-treated mice is similar to the phenotype of stem cells found in the fetal liver and to the phenotype of transiently repopulating progenitors in normal bone marrow. We found that cell cycle is induced concomitantly with these physical changes, and within 2 days as many as 29% of the stem-cell population is in the S/G2/M phases of the cell cycle. Furthermore, when examined at a clonal level, we found that 5-FU did not appear to eliminate many of the transient, multipotent progenitors from the bone marrow that were found to be copurified with long-term repopulating, activated stem cells. These results demonstrate the sensitivity of the hematopoietic system to changes in its homeostasis and correlate the expression of several important surface molecules with the activation state of HSCs.
已有研究表明，相当一部分造血干细胞（HSCs）对细胞毒性药物如5-氟尿嘧啶（5-FU）具有抗性。5-FU被认为可清除骨髓中许多快速分裂、分化程度更高的祖细胞，并提供相对富集的最原始造血祖细胞群体。尽管已描述了5-FU富集的祖细胞群体与正常骨髓祖细胞群体之间的差异，但尚不清楚这些差异是否反映了5-FU所揭示的最原始干细胞的特征，或者干细胞群体本身是否发生了变化。在此，我们研究了5-FU处理前后骨髓中干细胞的一些特性，并确定了干细胞群体中与激活相关的几种变化。我们发现，长期重建造血干细胞的生长因子受体c-kit表达降低了10倍，而整合素Mac-1（CD11b）的表达增加。这些变化在5-FU处理后24小时就开始出现，并在2至3天内最为明显。从5-FU处理的小鼠中分离出的造血干细胞的这种激活表型类似于胎儿肝脏中发现的干细胞表型以及正常骨髓中短暂重建造血祖细胞的表型。我们发现细胞周期与这些物理变化同时被诱导，并且在2天内多达29%的干细胞群体处于细胞周期的S/G2/M期。此外，在克隆水平上进行检测时，我们发现5-FU似乎并未清除骨髓中许多与长期重建造血、激活的干细胞共纯化的短暂、多能祖细胞。这些结果证明了造血系统对其稳态变化的敏感性，并将几种重要表面分子的表达与造血干细胞的激活状态相关联。
