Abstract 13777: NADPH oxidase2 Regulates Hematopoietic Stem Cell Niche to Promote Resolution of Inflammation during Neovascularization and Tissue Repair after Ischemic Injury
Stem cell niches, the discrete microenvironments in which the stem cells reside, regulate stem cell activity. Committed stem cell progeny is indispensable components of the niche. After tissue injury, hematopoietic stem cells (HSCs) may directly respond to damage-associated signals to produce inflammatory monocytes. Resolution of inflammation is important repair process after injury; however, underlying mechanisms by which HSC inflammatory differentiation contributes to this process remain unknown. Here we show that, in hindlimb ischemia model, mice lacking NADPH oxidase 2 (Nox2), a major source of reactive oxygen species (ROS) for hematopoietic cells, show impaired angiogenesis (38%) and tissue repair (55% decrease in muscle regeneration) with prolonged infiltration of Gr-1+ inflammatory monocyte (3.8-fold). This is associated with increased ratio of inflammatory (Gr-1+)/healing (Gr-1-) monocyte in ischemic tissue (11.5-fold) and peripheral blood (4.7-fold) as well as hyper development of Gr-1+ cells in bone marrow (BM) (2.4-fold) and spleen (8-fold) in Nox2-/- mice. These results suggest that Nox2-derived ROS are required for resolution of inflammation. Adoptive transfer of Nox2+/+ Gr-1+ cells in Nox2-/- mice sufficiently induces the resolution of inflammation (40% decrease in Gr-1+/Gr-1- ratio). In situ detection of ROS reveals that Gr-1+ cells produce Nox2-dependent ROS in BM after hindlimb ischemia. In vitro, HSC differentiation into inflammatory monocytes upon activation of TLR4, a key receptor for tissue damage signals, is enhanced in Nox2-/- HSCs, which is inhibited by co-culture with Gr-1+ cells in a Nox2- and extracellular ROS- dependent manner. The phosphorylation of Src family kinase, Lyn, a recently identified sensor for extracellular ROS, is inhibited in Nox2-/- BM cells upon TLR4 activation. Lyn-/- HSCs exhibit the similar enhancement in their differentiation into inflammatory monocytes. In summary, this study uncovers a novel negative feedback mechanism against persistent inflammatory response after acute ischemic injury through activation of Nox2-ROS-Lyn pathway in HSC niche by their progeny. This may lead to novel therapeutic strategies for ischemic cardiovascular diseases with hyperinflammatory background.
- Stem cells
- Reactive oxygen intermediates
- Ischemic heart disease
- Stem cell and atherosclerosis
- © 2012 by American Heart Association, Inc.