Fernandez Luis, Rodriguez Sonia, Huang Hui, Chora Angelo, Fernandes Jacquenilson, Mumaw Christin, Cruz Eugenia, Pollok Karen, Cristina Filipa, Price Joanne E, Ferkowicz Michael J, Scadden David T, Clauss Matthias, Cardoso Angelo A, Carlesso Nadia
Center of Regenerative Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Mass., USA.
Exp Hematol. 2008 May;36(5):545-558. doi: 10.1016/j.exphem.2007.12.012.
Homeostasis of the hematopoietic compartment is challenged and maintained during conditions of stress by mechanisms that are poorly defined. To understand how the bone marrow (BM) microenvironment influences hematopoiesis, we explored the role of Notch signaling and BM endothelial cells in providing microenvironmental cues to hematopoietic cells in the presence of inflammatory stimuli.
The human BM endothelial cell line (BMEC) and primary human BM endothelial cells were analyzed for expression of Notch ligands and the ability to expand hematopoietic progenitors in an in vitro coculture system. In vivo experiments were carried out to identify modulation of Notch signaling in BM endothelial and hematopoietic cells in mice challenged with tumor necrosis factor-alpha (TNF-alpha) or lipopolysaccharide (LPS), or in Tie2-tmTNF-alpha transgenic mice characterized by constitutive TNF-alpha activation.
BM endothelial cells were found to express Jagged ligands and to greatly support progenitor's colony-forming ability. This effect was markedly decreased by Notch antagonists and augmented by increasing levels of Jagged2. Physiologic upregulation of Jagged2 expression on BMEC was observed upon TNF-alpha activation. Injection of TNF-alpha or LPS upregulated three- to fourfold Jagged2 expression on murine BM endothelial cells in vivo and resulted in increased Notch activation on murine hematopoietic stem/progenitor cells. Similarly, constitutive activation of endothelial cells in Tie2-tmTNF-alpha mice was characterized by increased expression of Jagged2 and by augmented Notch activation on hematopoietic stem/progenitor cells.
Our results provide the first evidence that BM endothelial cells promote expansion of hematopoietic progenitor cells by a Notch-dependent mechanism and that TNF-alpha and LPS can modulate the levels of Notch ligand expression and Notch activation in the BM microenvironment in vivo.
在应激条件下，造血系统的稳态受到挑战并通过定义不清的机制得以维持。为了解骨髓（BM）微环境如何影响造血，我们探讨了Notch信号通路和BM内皮细胞在炎症刺激存在时向造血细胞提供微环境信号中的作用。
分析人BM内皮细胞系（BMEC）和原代人BM内皮细胞Notch配体的表达情况以及在体外共培养系统中扩增造血祖细胞的能力。进行体内实验，以确定在受到肿瘤坏死因子-α（TNF-α）或脂多糖（LPS）攻击的小鼠中，或在以TNF-α持续激活为特征的Tie2-tmTNF-α转基因小鼠中，BM内皮细胞和造血细胞中Notch信号通路的调节情况。
发现BM内皮细胞表达锯齿状配体，并极大地支持祖细胞的集落形成能力。Notch拮抗剂可显著降低这种作用，而增加Jagged2水平则可增强该作用。在TNF-α激活后，观察到BMEC上Jagged2表达的生理性上调。注射TNF-α或LPS可使小鼠体内BM内皮细胞上Jagged2表达上调三到四倍，并导致小鼠造血干/祖细胞上Notch激活增加。同样，Tie2-tmTNF-α小鼠中内皮细胞的持续激活表现为Jagged2表达增加以及造血干/祖细胞上Notch激活增强。
我们的结果首次证明，BM内皮细胞通过Notch依赖性机制促进造血祖细胞的扩增，并且TNF-α和LPS可在体内调节BM微环境中Notch配体表达水平和Notch激活。
