Oral Presentation Australian Society for Medical Research Annual Scientific Meeting 2016

Suppression of medullar erythropoiesis in response to bacterial lipopolysaccharides (LPS) involves two distinct TLR4-dependent mechanisms with contrasted requirements for G-CSF receptors (#7)

Kavita Bisht 1 , Rebecca Jacobsen 1 , Bianca Nowlan 1 , Crystal McGirr 1 , Marion Brunck 1 , Thomas Keech 1 , Ingrid Winkler 1 , Jean-Pierre Levesque 1
  1. Mater Research Institute University of Queensland, Woolloongabba, QLD, Australia

Erythropoiesis is a highly controlled process partly regulated by the central erythroblastic island macrophage (EI MΦ) which provides iron, growth factors and mediates enucleation of erythroblasts1,2. As macrophages are key effectors of inflammation3, we investigated the effect of bacterial LPS in vivo on erythropoiesis and EI MΦ, defined as CD11b+ F4/80+ VCAM1+ CD169+Ly6G+ in mice4. C57BL/6 mice were injected with 2.5 mg/kg/day LPS for 2 days. LPS administration caused whitening of the bone marrow (BM) with decreased numbers of basophilic (9-fold), polychromatic (3.7-fold), orthochromatic erythroblasts (2.2-fold) and reticulocytes (2.5-fold) and EI MΦ in the BM. This loss of medullar erythropoiesis was compensated by increased number of EI MΦ (13.6-fold), pro-erythroblasts (1.5-fold), polychromatic (1.9-fold), orthochromatic (3.2-fold) and reticulocytes (2.3-fold) in the spleen. As this phenotype resembled suppression of medullar erythropoiesis following G-CSF treatment, we examined whether the mechanism could be indirect via endogenous G-CSF release. LPS induced a transient 80-fold increase in G-CSF concentration in the blood from 123pg/mL to 10ng/ml. LPS was also administered to TLR4 KO and G-CSF receptor (GCSFR) KO mice. These LPS-mediated responses were abrogated in TLR4 KO mice demonstrating that erythropoiesis suppression is TLR4-dependant. However responses in GCSFR KO mice were more contrasted. EI MΦ numbers did not change in GCSFR KO mice and medullar erythropoiesis was still suppressed in KO mice. To further understand how BM erythrocytes could be increased whilst erythropoiesis is suppressed in LPS-treated GCSFR KO mice, we measured vascular leakage by injecting Evans Blue. Blood plasma/femur volume in the BM of LPS-treated GCSFR KO mice was 2.9-fold higher compared to LPS-treated wild-type mice, suggesting that GCSFR-mediated signaling is necessary to maintain the integrity of the BM vasculature in response to LPS. In conclusion LPS-mediated medullar erythropoiesis suppression involves at least two different TLR4-dependent mechanisms in regards to their requirement for GCSFR.

  1. Yu, V. W. Scadden, D. T. Hematopoietic Stem Cell and Its Bone Marrow Niche Curr Top Dev Biol, 18, 2016
  2. Manwani, D. Bieker, J. J. The erythroblastic island, Curr Top Dev Biol, 82, 2008
  3. Burberry, A. et al. Infection mobilizes hematopoietic stem cells through cooperative NOD-like receptor and Toll-like receptor signaling, Cell Host Microbe, 15, 2015
  4. Jacobsen, R. N. et al. Mobilization with granulocyte colony-stimulating factor blocks medullar erythropoiesis by depleting F4/80(+)VCAM1(+)CD169(+)ER-HR3(+)Ly6G(+) erythroid island macrophages in the mouse, Exp Hematol, 42, 2014