Department of Pharmacology, Center for Lung and Vascular Biology, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
Stem Cells. 2012 May;30(5):923-34. doi: 10.1002/stem.1048.
Bone marrow (BM) microenvironment, which is regulated by hypoxia and proteolytic enzymes, is crucial for stem/progenitor cell function and mobilization involved in postnatal neovascularization. We demonstrated that NADPH oxidase 2 (Nox2)-derived reactive oxygen species (ROS) are involved in postischemic mobilization of BM cells and revascularization. However, role of Nox2 in regulating BM microenvironment in response to ischemic injury remains unknown. Here, we show that hindlimb ischemia of mice increases ROS production in both the endosteal and central region of BM tissue in situ, which is almost completely abolished in Nox2 knockout (KO) mice. This Nox2-dependent ROS production is mainly derived from Gr-1(+) myeloid cells in BM. In vivo injection of hypoxyprobe reveals that endosteum at the BM is hypoxic with high expression of hypoxia-inducible factor-1α in basal state. Following hindlimb ischemia, hypoxic areas and HIF-1α expression are expanded throughout the BM, which is inhibited in Nox2 KO mice. This ischemia-induced alteration of Nox2-dependent BM microenvironment is associated with an increase in vascular endothelial growth factor expression and Akt phosphorylation in BM tissue, thereby promoting Lin(-) progenitor cell survival and expansion, leading to their mobilization from BM. Furthermore, hindlimb ischemia increases proteolytic enzymes membrane type 1-matrix metalloproteinase (MMP) expression and MMP-9 activity in BM, which is inhibited in Nox2 KO mice. In summary, Nox2-dependent increase in ROS plays a critical role in regulating hypoxia expansion and proteolytic activities in BM microenvironment in response to tissue ischemia. This in turn promotes progenitor cell expansion and reparative mobilization from BM, leading to postischemic neovascularization and tissue repair.
骨髓（BM）微环境受缺氧和蛋白水解酶调节，对于参与出生后新生血管形成的干细胞/祖细胞功能和动员至关重要。我们证明，NADPH 氧化酶 2（Nox2）衍生的活性氧（ROS）参与了 BM 细胞的缺血后动员和再血管化。然而，Nox2 在调节 BM 微环境以响应缺血性损伤中的作用尚不清楚。在这里，我们显示小鼠后肢缺血会增加 BM 组织原位骨内膜和中央区域的 ROS 产生，而在 Nox2 敲除（KO）小鼠中几乎完全消除。这种 Nox2 依赖性 ROS 产生主要源自 BM 中的 Gr-1(+)髓样细胞。体内注射缺氧探针显示，BM 的骨内膜在基础状态下呈低氧状态，缺氧诱导因子-1α（HIF-1α）高表达。在后肢缺血后，低氧区域和 HIF-1α 表达在整个 BM 中扩展，而在 Nox2 KO 小鼠中受到抑制。这种缺血诱导的 Nox2 依赖性 BM 微环境改变与 BM 组织中血管内皮生长因子表达和 Akt 磷酸化增加有关，从而促进 Lin(-)祖细胞的存活和扩增，导致它们从 BM 中动员。此外，后肢缺血会增加 BM 中膜型 1-基质金属蛋白酶（MMP）的表达和 MMP-9 活性，而在 Nox2 KO 小鼠中受到抑制。总之，Nox2 依赖性 ROS 增加在调节组织缺血时 BM 微环境中的低氧扩展和蛋白水解活性中起关键作用。这反过来又促进了祖细胞的扩增和修复性动员，导致缺血后新生血管形成和组织修复。
