Medical Clinic and Policlinic I University Hospital, Dresden, Germany.
Haematologica. 2010 Apr;95(4):542-50. doi: 10.3324/haematol.2009.010736. Epub 2010 Feb 9.
Hematopoietic stem cells located in the bone marrow interact with a specific microenvironment referred to as the stem cell niche. Data derived from ex vivo co-culture systems using mesenchymal stromal cells as a feeder cell layer suggest that cell-to-cell contact has a significant impact on the expansion, migratory potential and 'stemness' of hematopoietic stem cells. Here we investigated in detail the spatial relationship between hematopoietic stem cells and mesenchymal stromal cells during ex vivo expansion.
In the co-culture system, we defined three distinct localizations of hematopoietic stem cells relative to the mesenchymal stromal cell layer: (i) those in supernatant (non-adherent cells); (ii) those adhering to the surface of mesenchymal stromal cells (phase-bright cells) and (iii) those beneath the mesenchymal stromal cells (phase-dim cells). Cell cycle, proliferation, cell division and immunophenotype of these three cell fractions were evaluated from day 1 to 7.
Phase-bright cells contained the highest proportion of cycling progenitors during co-culture. In contrast, phase-dim cells divided much more slowly and retained a more immature phenotype compared to the other cell fractions. The phase-dim compartment was soon enriched for CD34(+)/CD38(-) cells. Migration beneath the mesenchymal stromal cell layer could be hampered by inhibiting integrin beta1 or CXCR4.
Our data suggest that the mesenchymal stromal cell surface is the predominant site of proliferation of hematopoietic stem cells, whereas the compartment beneath the mesenchymal stromal cell layer seems to mimic the stem cell niche for more immature cells. The SDF-1/CXCR4 interaction and integrin-mediated cell adhesion play important roles in the distribution of hematopoietic stem cells in the co-culture system.
位于骨髓中的造血干细胞与一个特定的微环境相互作用，这个微环境被称为干细胞龛。来自使用间充质基质细胞作为饲养细胞层的体外共培养系统的数据表明，细胞间接触对造血干细胞的扩增、迁移潜力和“干性”有重大影响。在这里，我们详细研究了造血干细胞与间充质基质细胞在体外扩增过程中的空间关系。
在共培养系统中，我们将造血干细胞相对于间充质基质细胞层的三个不同定位定义为：（i）存在于上清液中的细胞（非贴壁细胞）；（ii）黏附在间充质基质细胞表面的细胞（相亮细胞）和（iii）位于间充质基质细胞下方的细胞（相暗细胞）。从第 1 天到第 7 天，我们评估了这三个细胞群的细胞周期、增殖、细胞分裂和免疫表型。
相亮细胞在共培养过程中包含了最高比例的循环祖细胞。相比之下，相暗细胞的分裂速度要慢得多，并且与其他细胞群相比，保持了更不成熟的表型。相暗细胞群很快就富含 CD34(+)/CD38(-)细胞。通过抑制整合素β1 或 CXCR4 可以阻碍细胞向间充质基质细胞层下迁移。
我们的数据表明，间充质基质细胞表面是造血干细胞增殖的主要部位，而间充质基质细胞层下方的隔室似乎模拟了更不成熟细胞的干细胞龛。SDF-1/CXCR4 相互作用和整合素介导的细胞黏附在共培养系统中造血干细胞的分布中发挥重要作用。
