D'Ippolito Gianluca, Diabira Sylma, Howard Guy A, Roos Bernard A, Schiller Paul C
Geriatric Research, Education, and Clinical Center, and Research Service, Veterans Affairs Medical Center, Miami, FL 33125, USA.
Bone. 2006 Sep;39(3):513-22. doi: 10.1016/j.bone.2006.02.061. Epub 2006 Apr 17.
We recently reported the isolation of a unique subpopulation of human stromal cells from bone marrow (BM) termed marrow-isolated adult multilineage inducible (MIAMI) cells, capable of differentiating in vitro into mature-like cells from all three germ layers. The oxygen tension (pO2) in BM ranges from 1 to 7%, which prompted us to examine the role of pO2 in regulating the capacity of MIAMI cells both to self-renew and maintain their pluripotentiality (stemness) or to progress toward osteoblastic differentiation. MIAMI cells were grown under low-pO2 conditions (1, 3, 5, and 10% oxygen) or air (21% oxygen). The proliferation rate of cells exposed to 3% oxygen (3 days) increased, resulting in cell numbers more than threefold higher than those of cells exposed to air (at 7 days). In cells grown under osteoblastic differentiation conditions, the expression of the osteoblastic markers osteocalcin, bone sialoprotein, osterix, and Runx2 and alkaline phosphatase activity was upregulated when incubated in air; however, it was blocked at low (3%) pO2. Similarly, biomineralization of long-term cell cultures was high under osteoblastic differentiation conditions in air but was undetectable at low (3%) pO2. In contrast, low pO2 upregulated mRNAs for OCT-4, REX-1, telomerase reverse transcriptase, and hypoxia-inducible factor-1 alpha, and increased the expression of SSEA-4 compared to air. Moreover, the expression of embryonic stem cell markers was sustained even under osteogenic culture conditions. Similar results were obtained using commercially available marrow stromal cells. We hypothesize a physiological scenario in which primitive MIAMI cells self-renew while localized to areas of low pO2 in the bone marrow, but tend to differentiate toward osteoblasts when they are located closer to blood vessels and exposed to higher pO2. Our results strongly suggest that maintaining developmentally primitive human cells in vitro at low pO2 would be more physiological and favor stemness over differentiation.
我们最近报道了从骨髓（BM）中分离出一种独特的人类基质细胞亚群，称为骨髓分离的成年多谱系诱导（MIAMI）细胞，它能够在体外分化为来自所有三个胚层的成熟样细胞。骨髓中的氧张力（pO2）范围为1%至7%，这促使我们研究pO2在调节MIAMI细胞自我更新和维持其多能性（干性）或向成骨细胞分化能力方面的作用。MIAMI细胞在低pO2条件（1%、3%、5%和10%氧气）或空气（21%氧气）中培养。暴露于3%氧气（3天）的细胞增殖率增加，导致细胞数量比暴露于空气（7天）的细胞高出三倍以上。在成骨细胞分化条件下培养的细胞中，当在空气中培养时，成骨细胞标志物骨钙素、骨唾液蛋白、osterix和Runx2的表达以及碱性磷酸酶活性上调；然而，在低（3%）pO2时被阻断。同样，在空气中成骨细胞分化条件下长期细胞培养的生物矿化程度很高，但在低（3%）pO2时无法检测到。相比之下，与空气相比，低pO2上调了OCT-4、REX-1、端粒酶逆转录酶和缺氧诱导因子-1α的mRNA，并增加了SSEA-4的表达。此外，即使在成骨培养条件下，胚胎干细胞标志物的表达也得以维持。使用市售的骨髓基质细胞也获得了类似的结果。我们推测了一种生理情况，即原始的MIAMI细胞在定位于骨髓中低pO2区域时自我更新，但当它们更靠近血管并暴露于较高pO2时，倾向于向成骨细胞分化。我们的结果强烈表明，在体外低pO2条件下维持发育原始的人类细胞更符合生理，并且有利于干性而非分化。
