title: Interleukin-4 and interleukin-13 stimulate the osteoclast inhibitor osteoprotegerin by human endothelial cells through the STAT6 pathway.
abstract: BACKGROUND
  Endothelial cells of the bone vasculature modulate development, remodeling, and repair of bone by secreting osteotropic cytokines and hormones, which can act on osteoblastic and osteoclastic lineage cells. RANKL is the essential factor for differentiation, activation, and survival of osteoclasts, whereas osteoprotegerin (OPG) is a soluble decoy receptor and inhibitor for RANKL.
  
  
  METHODS
  In this study, we analyzed the regulation of OPG by T helper 2 (Th2) cytokines interleukin (IL)-4 and the closely related IL-13 in human umbilical vein endothelial cells (HUVECs), the underlying signaling pathway, and its functional relevance on osteoclastic resorption.
  
  
  RESULTS
  IL-4 and IL-13 induced OPG mRNA levels and protein secretion in HUVEC by up to 4-fold in a dose- and time-dependent fashion (maximum effect after 48 h and at 10 ng/ml). Activation of the transcription factor STAT6 preceded IL-4-induced OPG expression, and blockade of IL-4-induced STAT6 activation by the phospholipase C-specific inhibitor D609 decreased OPG expression. Soluble IL-4 receptor (sIL-4R) dose-dependently abolished both IL-4-induced STAT6 phosphorylation and OPG expression. RANKL stimulated the activity of osteoclasts, which was antagonized by HUVEC-derived supernatant containing OPG. The inhibitory effect on osteoclastogenesis was completely and specifically abrogated by a neutralizing OPG antibody in unstimulated HUVEC supernatant and partially in IL-4-stimulated HUVEC supernatant.
  
  
  CONCLUSIONS
  In summary, IL-4 and IL-13 induced OPG expression through activation of STAT6 in endothelial cells, and HUVEC-derived OPG is an IL-4/IL-13-induced inhibitor of osteoclastic resorption. These data underline the impact of Th2 cytokines on bone resorption through modulation of endothelial cell-derived cytokines.
authors.affiliation: Department of Medicine, Philipps-University, Marburg, Germany.
authors.forename: Nicola C
authors.initials: NC
authors.lastname: Stein
authors.forename: Carmen
authors.initials: C
authors.lastname: Kreutzmann
authors.forename: Sara-Pia
authors.initials: SP
authors.lastname: Zimmermann
authors.forename: Ute
authors.initials: U
authors.lastname: Niebergall
authors.forename: Lars
authors.initials: L
authors.lastname: Hellmeyer
authors.forename: Claudia
authors.initials: C
authors.lastname: Goettsch
authors.forename: Michael
authors.initials: M
authors.lastname: Schoppet
authors.forename: Lorenz C
authors.initials: LC
authors.lastname: Hofbauer
mesh_terms: D015152:Blotting, Northern; D015153:Blotting, Western; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D018793:Interleukin-13 / Q000502:physiology*; D015847:Interleukin-4 / Q000502:physiology*; D053244:Osteoprotegerin / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D050800:STAT6 Transcription Factor / Q000502:physiology*
chemical_list: D018793:Interleukin-13; D053244:Osteoprotegerin; D012333:RNA, Messenger; D050800:STAT6 Transcription Factor; C494101:STAT6 protein, human; D015847:Interleukin-4