Abstract 18411: NADPH oxidase Nox2 is Involved in Non-inflammatory Myeloid Cell Expansion in Bone Marrow after Hindlimb Ischemia: Mechanism for Reparative Angiogenesis
Neovascularization is an important repair process that depends on angiogenesis and inflammation associated with pro- and non-inflammatory monocytes/macrophages. We previously showed that NADPH oxidase Nox2-derived reactive oxygen species (ROS) play an important role in bone marrow (BM) vascular progenitor mobilization, which contributes to post-ischemic neovascularization. Paradoxically, Nox2 deficiency shows enhanced pro-inflammatory response in rodents and human. We thus investigated the role of Nox2 in monocyte production in BM in response to hindlimb ischemia to address the mechanism for Nox2-dependent angiogenic BM cells mobilization. Using in situ ROS measurement with DHE injection and immunofluorescence, here we show that CD45+ hematopoietic cells in the BM have high ROS levels after hindlimb ischemia in WT mice, while it is blunted in Nox2 knockout (KO) mice. However, FACS analysis of BM cells reveals that Gr-1hi inflammatory subset (day 1) and HSCs (Lin-cKit+Sca1+)(day 3) are rather expanded after hindlimb ischemia in Nox2 KO mice to the similar extent to WT mice. Furthermore, HSCs differentiation into Gr-1hi inflammatory cells in response to lipopolysaccharide is largely augmented in Nox2 KO HSCs (2.7-fold), while inflammatory cell signaling (increased p-IRAK4 and decreased inhibitor of NF-kB, IkB-α) is enhanced in Nox2 KO BM after ischemia. These suggest that Nox2 KO BM contributes to augmented inflammatory response by promoting myeloid differentiation of HSCs into inflammatory cells. By contrast, ischemia-induced increase in non-inflammatory Gr-1lo monocytes is inhibited in BM of Nox2 KO mice. They are associated with sustained increase in circulatory Gr-1hi monocytosis (3.5-fold) as well as decrease in circulating non-inflammatory cell subsets Gr-1lo monocytes (74 %) in Nox2 KO mice. In summary, Nox2 negatively regulates expansion of pro-inflammatory myeloid cell while positively regulates non-inflammatory myeloid cell in BM. This in turn facilitates mobilization of “non-inflammatory” myeloid cells, which may contribute to reparative angiogenesis.
- © 2010 by American Heart Association, Inc.