Abstract 13490: NADPH Oxidase Nox2 Limits Hematopoietic Stem Cell Differentiation Toward Pro-Inflammatory Myeloid Cells Through Activation of AMP kinase: Role in Reparative Inflammatory Angiogenesis
Reactive oxygen species (ROS) are important mediators of hematopoietic stem cells (HSCs) function. We previously demonstrated that NADPH oxidase Nox2-derived ROS play an important role in post-ischemic reparative angiogenesis. Although inflammatory response is closely linked to Nox-derived ROS, their role in HSCs function in response to ischemic injury is poorly understood. Using in vitro hematopoietic stem cell (HSC; cKithiSca1+Lin- in bone marrow (BM)) culture, here we show that HSC differentiation into Gr-1hi inflammatory monocytes in response to toll-like receptor4 (TLR4) ligand is augmented in Nox2-/- HSCs (2.3-fold), which is prevented by co-culture with wild type (WT)-HSCs (65 %). The co-culture with immature inflammatory CD11b+/Gr-1+ monocytes from Nox2-/- mice also enhances the differentiation of WT-HSCs (1.7-fold) as compared to those from WT mice, suggesting the suppressing role of Nox2-derived ROS in HSC myeloid differentiation. Mechanistically, phosphorylation of ROS-sensitive and anti-inflammatory kinase, AMPK induced by TLR4 ligand is markedly reduced in Nox2-/- BM-derived monocytes (80%) and activation of AMPK with AICAR inhibits pro-inflammatory myeloid differentiation of HSCs (52%). These suggest that Nox2-derived ROS activate AMPK, thereby limiting HSCs differentiation. In vivo, Nox2-/- mice increase Gr-1hi inflammatory monocytes in the ischemic muscle (3.8-fold), circulation (4.3-fold), the spleen (8-fold) and the BM (2.4-fold) following femoral artery ligation, while WT mice increase reparative Gr-1lo monocytes. This is associated with prolonged increase of pro-inflammatory cytokines, TNFalpha (2.2-fold) and IL-6 (1.2-fold) as well as reduced maturated arterioles (38%) in ischemic tissues of Nox2-/- mice. The direct dye injection reveals Nox2-dependent increase in in situ O2- in the BM Gr-1+ cells following ischemic injury, which may limit HSC differentiation in BM microenvironment. In summary, Nox2-derived ROS limit HSC differentiation toward pro-inflammatory monocytes by activating anti-inflammatory kinase AMPK, which may ensure the Gr-1hi to Gr-1lo transition of monocyte recruitment and contribute to reparative angiogenesis and tissue repair in response to ischemic injury.
- © 2011 by American Heart Association, Inc.