Activation of toll‐like receptors 2 and 4 on CD 34 + cells increases human megakaryo/thrombopoiesis induced by thrombopoietin

D'ATRI, LINA PAOLA; RODRÍGUEZ, CAMILA SOFÍA; MIGUEL, CAROLINA PAULA; POZNER, ROBERTO GABRIEL; ORTIZ WILCZYÑSKI, JUAN MANUEL; NEGROTTO, SOLEDAD; CARRERA-SILVA, EUGENIO ANTONIO; HELLER, PAULA GRACIELA; SCHATTNER, MIRTA

JOURNAL OF THROMBOSIS AND HAEMOSTASIS

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2019

1538-7933

Background: Platelet Toll‐like receptor (TLR)2/4 are key players in amplifying thehost immune response; however, their role in human megakaryo/thrombopoiesis hasnot yet been defined.Objectives: We evaluated whether Pam3CSK4 or lipopolysaccharide (LPS), TLR2/4ligands respectively, modulate human megakaryocyte development and plateletproduction.Methods: CD34+ cells from human umbilical cord were stimulated with LPS orPam3CSK4 with or without thrombopoietin (TPO).Results: CD34+ cells and megakaryocytes express TLR2 and TLR4 at both RNA andprotein level; however, direct stimulation of CD34+ cells with LPS or Pam3CSK4 hadno effect on cell growth. Interestingly, both TLR ligands markedly increased TPO‐in‐duced CD34+ cell proliferation, megakaryocyte number and maturity, proplatelet andplatelet production when added at day 0. In contrast, this synergism was not observedwhen TLR agonists were added 7 days after TPO addition. Interleukin‐6 (IL‐6) releasewas observed upon CD34+ or megakaryocyte stimulation with LPS or Pam3CSK4 butnot with TPO and this effect was potentiated in combination with TPO. The increasedproliferation and IL‐6 production induced by TPO + LPS or Pam3CSK4 were sup‐pressed by TLR2/4 or IL‐6 neutralizing antibodies, as well as by PI3K/AKT and nuclearfactor‐κB inhibitors. Additionally, increased proplatelet and platelet production wereassociated with enhanced nuclear translocation of nuclear factor‐E2. Finally, the su‐pernatants of CD34+ cells stimulated with TPO+LPS‐induced CFU‐M colonies.Conclusions: Our data suggest that the activation of TLR2 and TLR4 in CD34+ cellsand megakaryocytes in the presence of TPO may contribute to warrant platelet provi‐sion during infection episodes by an autocrine IL‐6 loop triggered by PI3K/NF‐κB axes.